1. Field of the Invention
The present invention relates to a sealing structure using an O-ring for preventing fluid leakage.
2. Description of the Invention
Various sealing structures have been developed to prevent leakage of hydrogen from a hydrogen tank (storage body) mounted in a fuel cell vehicle that stores high pressure hydrogen inside or prevent leakage of oil from a section of a hydraulically-operated apparatus which makes reciprocating movement.
For example, the hydrogen tank has a cylindrical outer shape and has an end provided with a cylindrical connector portion (reception member) for a valve body (insertion member) to be inserted in. The connector portion has an inner circumferential surface with an inner threaded portion formed therein. The valve body has an outer circumferential surface with an outer threaded portion formed thereon. When the connector portion is fitted into the valve body by engaging those portions with each other, an annular accommodation region is formed for accommodating an O-ring to prevent leakage of hydrogen from the hydrogen tank. Further, in some cases, a back-up ring or rings are fitted inside the accommodation region to prevent damage to the O-ring caused by the O-ring being caught in a clearance between the connector portion and the valve body.
Japanese Patent No. 3543617 discloses a sealing device including a shaft (insertion member), a shaft hole (reception member), a sealing ring (O-ring), a back-up ring. An annular attachment groove is formed in either one of the shaft and the shaft hole with the sealing ring and the back-up ring fitted in the attachment groove. When a pressure is applied to the attachment groove from a higher pressure side, there is a clearance between an inner wall face, on a lower pressure side, of the attachment groove and a surface, on the lower pressure side, of the back-up ring. According to the sealing device of Japanese Patent No. 3543617, it is possible to prevent damage to the sealing ring and thereby favorably maintain sealing performances.
Japanese Unexamined Patent Application Publication No. 2002-161983 discloses a sealing device including a shaft (insertion member) and a housing (reception member) coaxially fitted with each other, two back-up rings, and a sealing ring (O-ring) sandwiched between the two back-up rings. The sealing ring and the back-up rings are fitted inside an annular attachment groove formed in either one of the shaft and the housing. Each back-up ring has a taper formed to come in total contact with and abut on each of tapers formed at both end portions of the attachment groove. According to the sealing device of Japanese Unexamined Patent Application Publication No. 2002-161983, it is possible to convert a pressure in the axial direction applied to each of the back-up rings into a radially outward force and a radially inward force to allow the back-up rings to fill in a clearance between the shaft and the housing and thereby prevent the O-ring from being caught in the clearance and being damaged.
In the sealing devices of Japanese Patent No. 3543617 and Japanese Unexamined Patent Application Publication No. 2002-161983, however, the annular attachment groove is formed only in either one of the insertion member and the reception member. Accordingly, there arises a problem that the insertion member and the reception member might collide with each other to be damaged when the insertion member is inserted into the reception member.
For example, in the sealing device (sealing structure) of Japanese Unexamined Patent Application Publication No. 2002-161983, as shown in FIG. 7A, a shaft (insertion member) 8 has an annular attachment groove 13. An O-ring 10 and two back-up rings 11, 12 are fitted into the annular attachment groove 13 and then the shaft 8 is inserted into a housing (reception member) 9.
In general, the outer diameter of the shaft 8 is made slightly smaller than the inner diameter of the housing 9 in cross section in consideration of ease of fitting of the shaft 8 into the housing 9 and manufacturing errors. However, it is difficult to insert the shaft 8 into the housing 9 with the central axes of the shaft 8 and the housing 9 in complete alignment to prevent the collision of the shaft 8 with the housing 9.
That is, as shown in FIG. 7B, when the shaft 8 of the sealing device is fitted into the housing 9, there is a high risk of the collision of the outer circumferential surface of the shaft 8 with the inner circumferential surface S of the housing 9, resulting in damage to the outer circumferential surface of the shaft 8 and to the inner circumferential surface S of the housing 9, that is, damage to a portion of the inner circumferential surface S of the housing 9 that corresponds to an accommodation region FI for accommodating an O-ring 10. This will cause the problem of insufficient sealing of the clearance by the O-ring 10, resulting in fluid leakage.
It is an object of the present invention to provide a sealing structure that permits easy fitting of the insertion member into the reception member and that prevents damage to the insertion member and the reception member.